This invention is in the field of integrated circuits and in the field of marking integrated circuits for tracking purposes.
There is a need in the semiconductor industry for a reliable method of marking integrated circuit die (xe2x80x9cchipsxe2x80x9d) to facilitate tracking of these devices after they are manufactured and sent to customers worldwide. For example, in instances where a customer detects an imperfection in a particular chip, or desires more chips that behave like a particular chip, the ability to ascertain the provenance of the chip and the conditions under which it was fabricated can constitute a competitive advantage for an integrated circuit manufacturer. Whereas, in the past, the marking of the chips on a particular wafer has been possible, it has been possible to only mark chips with a gross level of identification, since all of the chips on a wafer in a given lot of wafers of a particular type of integrated circuit are made with the same set of reticles or masks. Since, for a given level in the fabrication of the chip, that same reticle is stepped across the entire wafer, it has not been possible to give each individual chip its own identifying mark during the wafer fabrication process, where it is most cost efficient to do so. Thus, a problem with a particular chip can only also be traced back as far as the level of identification on the chip allows.
In addition, the continuing demand for smaller chips has put space at a premium and has complicated the task of marking. Typically, all of the wafers in a lot bear the same mark, indicating the device design type, year and month of manufacture, and perhaps the location of manufacture. The identifying mark is also typically large enough to be visually identified with a microscope, for example. As the demand for smaller chips is increasing, the space available for placing such information on each chip has diminished accordingly. For example, for a 1.5 mmxc3x971.5 mm device package, it is not unusual to have space sufficient on the chip for only about five identifying characters, three for the device type and two for the year and month of manufacture, for example. A defect in such a device can only be traced to the year and month in which the chip was made. In many cases, a manufacturer may have fabrication facilities all over the world and many thousands of wafers produced by each of those facilities a month, so much more detailed marking of such small chips is needed. It is clear that there is a need in the industry for better ways of marking integrated circuit die.
One embodiment of the invention is a method for marking a semiconductor wafer. The method includes the steps of: providing a reticle including liquid crystal pixels; positioning the semiconductor wafer in proximity to the reticle; directing radiation through a first plurality of the pixels onto a first location on the wafer; changing the relative positions of the semiconductor wafer and the reticle; and directing radiation through a second plurality of the pixels onto a second location on the wafer. The first plurality of pixels can be used to form a first mark and the second plurality of pixels can be used to form a second mark, wherein the second mark is different from the first mark. The marks can be made of a pattern of dots in order to save space. The pixels can be selected to form certain marks by using a computer to turn on or off a transistor that may be associated with each pixel.
Another embodiment is a system for marking a semiconductor wafer. The system includes a wafer mount; a radiation source in proximity to the wafer mount; a reticle which includes liquid crystal pixels and that is positionable between the radiation source and the wafer mount; and a mechanism for changing the relative positions of the reticle and the wafer mount. The radiation source can be non-coherent far-ultraviolet, near-ultraviolet, or visible sources, or a laser.
Still another embodiment of the invention includes a method for marking a semiconductor wafer. The method includes the step of providing a test probe tool. The tool includes a wafer chuck, a test head in proximity to the wafer chuck, a probe card attached to the test head, and a laser mounted on the tool. The method also includes the steps of mounting a semiconductor wafer on the wafer chuck; contacting a first location on the wafer with the probe card; making a first mark on the first location with the laser; changing the relative positions of the probe card and the wafer; contacting a second location on the wafer with the probe card; and making a second mark on the second location with the laser. The second mark is different from the first mark, and may include a pattern of dots that indicate the first and second locations on the wafer. The steps of contacting a first location on the wafer and making a first mark on the first location may be performed concurrently.
An advantage of the invention is that it allows for a chip-level custom identification mark for each chip on a wafer.